The present invention relates to refrigerated merchandisers, and specifically to anti-fog heat control for doors on refrigerated merchandisers.
Refrigerated merchandisers generally include a case defining a product display area for supporting and displaying food products to be visible and accessible through an opening in the front of the case. Refrigerated merchandisers are generally used in retail food store applications such as grocery or convenient stores or other locations where food product is displayed in a refrigerated condition. Some refrigerated merchandisers include doors to enclose the product display area of the case and reduce the amount of cold air released into the surrounding environment. The doors typically include one or more glass panels that allow a consumer to view the food products stored inside the case.
Existing refrigerated merchandisers display fresh and frozen food product in a product display area, and include glass doors to provide visibility of the food product and product accessibility to consumers. Often, condensed moisture accumulates on the exterior surface of the cold glass, which obscures viewing of the product in the merchandiser. The moisture in the relatively warm ambient air of the store can condense on the outside surface of the glass door. Similarly, moisture can condense on the cold inside surface of the glass door when the door is opened. Without heating, the condensation on the outside and inside of the glass door does not clear quickly and obscures the food product in the merchandiser. Long periods of obscured food product caused by condensation may detrimentally impact sales of the food product.
In doors with a single glass panel, condensation typically forms on the outer surface of the glass panel due to the cool outer surface being in communication with the ambient environment. In addition, fog often forms on the inner surface the glass panel due to the inner surface generally being in communication with the relatively cold product display area and then being exposed to the relatively humid air of the ambient environment when the door is opened. In doors with multiple glass panels (e.g. three glass panels), emissivity coatings along the panels inhibit heat transfer through the panels, thereby keeping the outer-most glass panel (i.e. the panel exposed to the ambient environment) warmer than the inner-most glass panel (i.e. the panel exposed to the product display area). In these multi-panel doors, condensation is less likely to occur on the warmer outer-most glass panel, but is still likely to occur on the colder inner-most glass panel when the door is opened.
Some glass doors include a resistive coating or semi-conductive film (e.g., tin-oxide) adhered or affixed to the glass door to remove condensation and fog. The resistive coating supplies heat to the glass door via current flow through the coating caused by a supply of electrical potential or electricity from the merchandiser. Typically, the heat applied to the glass door is controlled by a controller based on a duty cycle. These duty cycles are varied between an “on” state (i.e. heat applied to the glass door) and “off” state to regulate the time that heat is applied to the glass door, and are generally defined by the percentage of time that the duty cycle is in the “on” state. However, existing control systems regulate heat applied to glass doors based on a predetermined duty cycle that supplies electrical potential to the glass door based on the predetermined time that the duty cycle is in the “on” state. The time that the duty cycle is in the “on” state is regulated to limit energy use by the merchandiser. Once the duty cycle enters the “off” state, no electrical potential is supplied to the glass door. When the glass door is opened during the predetermined time that the duty cycle is in the “off” state, condensation may readily form on the interior and/or exterior of the glass door.
Conventional control systems cannot eliminate condensation that forms on the glass door when the duty cycle is in the “off” state. Instead, heat is applied to the glass door to remove condensation only when the duty cycle is in the “on” state. As such, the duty cycle regulated by conventional control systems can adversely affect elimination of condensation from the glass door due to a relatively long period of time between the glass door being opened and the duty cycle entering the “on” state. The inability of existing control systems to actively remove condensation from glass doors in response to formation of condensation allows condensation to remain on the glass doors for a long time, and detrimentally impacts the viewability of the food product.
Similarly, conventional control systems cannot compensate for multiple door openings that occur in a relatively short period of time to adequately clear condensation and fog from the glass doors. For example, when multiple door openings occur and the duty cycle is in the “off” state (i.e. no heat applied to the glass door), condensation can accumulate on the glass door. The condensation is not removed by the control system until the duty cycle enters the “on” state. Depending on the duty cycle, a relatively long period of time can elapse between the last of the multiple door openings and entry of the duty cycle into the “on” state. As a result, the glass door can remain obscured by condensation for a relatively long time.